1. Field of the Invention
This invention relates to numerical control systems, and more particularly, to the phase loop of a numerical control system.
2. Description of the Prior Art
The phase loop of prior art numerical control systems is clearly shown and explained in U.S. Pat. No. 3,519,904 and assigned to the same assignee as the assignee of the present invention. In this patent a clock oscillator is shown driving a reference counter and a command counter. The output from the reference counter is coupled to a phase splitter which separates the output of the reference counter into two signals 90.degree. apart. These signals are coupled via respective resolver supplies to respective stator windings of a resolver. The resolver has an armature which is responsive to movement of an object being controlled to generate an output waveform which is processed by a waveshaper to produce a square wave analog signal which is indicative of the actual position of the object. The square wave output signal of the command counter is displaced in phase with respect to the square wave output signal of the reference counter by a predetermined phase displacement which is indicative of the desired position of the object. The output signal from the command counter is then compared with the output signal from the waveshaper by a phase discriminator using standard analog techniques to produce an error analog signal that drives a servo amplifier, which amplifier in turn drives a motor to move the object in to a direction towards the desired position. In attempting to modernize servo systems, and, in particular, numerical control systems, it is hoped that a digital comparison between the above signals can be made.